In an internal combustion engine a boost in horsepower can be accomplished by forcing a more dense air/fuel charge into the cylinders with a supercharger. A supercharger can provide a dependable and affordable method of increasing horsepower and torque. A supercharger forces a more dense air/fuel mixture into an internal combustion engine's cylinders than the engine can draw in under normal conditions. This higher-energy mixture produces more power. Supercharging increases the engine's volumetric flow without increasing its displacement. Therefore, a supercharged small engine can produce the horsepower and torque of a relatively larger engine.
There are two basic blower systems used to force an air/fuel mixture into an internal combustion engine. These blowers are either a dynamic or a positive displacement equipment. Turbocharging, which is a dynamic process, places a turbine wheel in the exhaust flow of the engine. The turbine blades are directly connected to a centrifugal blower. One major disadvantage of a turbocharger is "turbo-lag." This is the delay that occurs after calling for power with the throttle before the rotational speed of the system spools up to deliver that power. An improperly sized or designed turbo system can rapidly over-boost and damage a spark-ignited internal combustion engine. The sizing of the turbocharger to the engine and the matching of the turbine size and design to impeller size and design are very critical. Additionally, the exhaust turbine tends to cool the exhaust gases thereby delaying the catalyst light-off of modern automotive emissions systems.
Centrifugal impeller type supercharging is a system having an impeller and a drive belt from the crankshaft operatively connected to a speed-increaser. A speed-increaser, either geared or gearless, is required to multiply the speed of the impeller. The delivery of a centrifugal impeller supercharger varies dramatically with its rotational speed, and is prone to under-boost at low speed and over-boost at high speed. An example of a centrifugal impeller supercharger is disclosed by M. Shirai in U.S. Pat. No. 5,158,427.
The most common positive displacement system is the "Roots blower". In this system, a belt-driven shaft drives two close-clearance rotors which are geared together. Each full rotation sweeps out a specific fixed volume, unlike the fan-like characteristics of a turbine device.